(a) Field
The invention relates to an optical structure, and more particularly, to an optical structure which is used to distribute light emitted from a light source of a direct type light emitting diode (“LED”) backlight unit and a backlight unit including the same.
(b) Description of the Related Art
A liquid crystal display (“LCD”) is one of flat panel displays which are widely used. In general, in a display panel of the LCD, a liquid crystal material is injected between an upper substrate on which a common electrode and a color filter are disposed, and a lower substrate on which a thin film transistor and a pixel electrode are disposed. Different electrical potentials are applied to the pixel electrode and the common electrode to generate an electric field to change the alignment of liquid crystal molecules in the liquid crystal material and adjust light transmittance to display an image on the display panel.
As a liquid crystal display panel of the LCD is a non-emissive light device, a backlight unit is generally equipped in the LCD to provide light to the liquid crystal display panel from the lower part of the liquid crystal display panel.
In the backlight unit, a cold cathode fluorescent lamp (“CCFL”) and a light emitting diode (“LED”) are generally used as a light source. In the related art, the CCFL which provides bright white light with low power consumption is mainly used. However, usage of an LED which has advantages such as excellent color reproducibility, long life-span, and low power consumption as compared with the CCFL, is being increased.
The backlight unit is classified into an edge type and a direct type in accordance with a position of the light source with respect to the liquid crystal display panel. In the edge type, a light source is disposed at a side of the liquid crystal display panel to provide light through a side of a light guide. In the direct type, the light source is disposed at a rear side of the liquid crystal display panel to provide light to the liquid crystal display panel. The direct type backlight unit has advantages of high light utilization coefficient, simple treatment, no limitation of size of the display panel, and relatively cheap cost, in comparison with the edge type backlight unit.